Drawing primitives cleanup (#13801)

* Remove unused using directives.

* Remove unused constants

* Assert on impossible value on first obtaining, rather than after
it should have been used.

* Remove unchecked context when can't overflow.

(Left some that match with neighbouring lines).

* Make init-only fields readonly.

* Consitently use expression bodies on single-expression members.

* Remove some redundant casts where the result is clear.

* Remove unnecessary qualifiers and make internal fields private when only accessed private.

* Move declaration of variables to where they are initialised.

* Replace statics with const, and remove obsolete comment.

3 files changed, 0 insertions, 5 deletions

diff --git a/src/System.Drawing.Primitives/tests/ColorTests.cs b/src/System.Drawing.Primitives/tests/ColorTests.cs
index 3b5df94e40..cde3411937 100644
--- a/src/System.Drawing.Primitives/tests/ColorTests.cs
+++ b/src/System.Drawing.Primitives/tests/ColorTests.cs
@@ -4,9 +4,7 @@
 
 using System.Collections.Generic;
 using System.Diagnostics;
-using System.IO;
 using System.Linq;
-using System.Runtime.Serialization.Formatters.Binary;
 using Xunit;
 
 namespace System.Drawing.Primitives.Tests
diff --git a/src/System.Drawing.Primitives/tests/RectangleFTests.cs b/src/System.Drawing.Primitives/tests/RectangleFTests.cs
index eff09fd59d..a989cdee31 100644
--- a/src/System.Drawing.Primitives/tests/RectangleFTests.cs
+++ b/src/System.Drawing.Primitives/tests/RectangleFTests.cs
@@ -2,7 +2,6 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-using System.Collections.Generic;
 using System.Globalization;
 
 using Xunit;
diff --git a/src/System.Drawing.Primitives/tests/SerializationTests.cs b/src/System.Drawing.Primitives/tests/SerializationTests.cs
index 533b7e78d8..e8c7cedd97 100644
--- a/src/System.Drawing.Primitives/tests/SerializationTests.cs
+++ b/src/System.Drawing.Primitives/tests/SerializationTests.cs
@@ -1,6 +1,4 @@
 using System.Collections.Generic;
-using System.IO;
-using System.Linq;
 using System.Runtime.Serialization.Formatters.Tests;
 using Xunit;